In prior art it is known to collect sunlight through absorption surfaces, such as solar collectors heating water, air, or any other form of medium. The medium is in general adapted to either be used, as warm water in a domestic application or as a heat transfer medium used to heat an indoor area, heated floor, or any other form of application area requiring heating. Solar collectors are further common for heating of water used for swimming pools both in public and private settings.
Solar collectors heating different sorts of mediums has been available on the market for a long time and the most common solution currently sold in the world are glazed solar collectors where the collectors utilize glass tubes to absorb heat. The market is dominated by two different techniques that both present options both for domestic and public use. Those two solutions are evacuated tube collectors and flat plate collectors, both glazed options.
In addition to the glazed solar collectors a segment of unglazed solar collectors are available as an in general cheaper alternative. Those solar collectors are almost exclusively sold on the North American, Brazilian, and Australian markets for the use of heating water in swimming pools. Due to the limited efficiency of such solutions are they overrepresented for private swimming pools installed by home owners. Even though those solar collectors are unglazed are their structural components fragile and easily broken. Those skilled in the art are aware of the vast problems with repairing and replacing such solutions.
There are multiple reasons for why the fragile solutions dominate the market of unglazed solar collectors, mostly corresponding to heat transfer rates and cost. In order for traditional unglazed solar collectors to gain a transfer rate between absorption surfaces of the solar collector and the medium inside considered sufficient those structures are normally produced with very thin material thickness. One trivial example that has been regularly available on the market is a black plastic bag that is filled with water and placed in the sun allowing the water to be heated. Those have in prior art for example been used to produce warm water for portable showers adapted for camping and boat vacations.
As described there are numerous of drawbacks with the existing technology of unglazed solar collectors, such as the fragileness, relatively bad efficiency, and an often unpleasant esthetical appearance. Similar problems of fragileness and unpleasant esthetical appearance also applies for most glazed solar collectors on the market and in addition are those solution normally more expensive resulting in a long investment term before the value created by the solar collectors corresponds to the invested value.
Furthermore, the aforementioned solutions, of both glazed and unglazed collectors, are in many cases adapted to be arranged for example on roofs or any similar structure, preferably where they are as inaccessible as possible in order to decrease the risk of damage. This is due to the fragile nature as previously described and because roofs and similar surfaces often provide a clear line between the sunrays and the solar collector for large portions of the day. Arranging solar collectors on roofs and similar areas that are in plain sight further increases the problems associated with such solutions. Architects and city planners are reluctant to install installations that are not part of the esthetical appearance of a building or construction. This causes problems with for example building permits which in many jurisdictions are required for visible solar collectors.
In prior art it is further known that heat transfer between the solar collector and the medium inside is essential for the efficacy of the solar collector. It is further known that the ambient temperature is affecting the efficiency and that the heat leakage between the ambient air and the medium shall be minimized in order to increase the efficacy. However, in general there is a relation between decreasing the leakage of heat with the transfer rate making thin structures the most suitable solution.
The person skilled in the art understands that glazed solar collectors are fragile constructions that need to be handled with care during installation and installed in a way that they are hard to access and thereby damage. However, the requirement for efficacy demands that the materials in the solar collectors are thin in order to utilize sufficient heat transfer between the absorption surface and the medium which has the effect that also the unglazed solar collectors become fragile.